Conventionally the fuel supply system of a Diesel engine comprises a fuel pump capable of delivering high output pressures of up to 1600 bar, an injector associated to each cylinder of the engine and a rail connecting the injector to the pump. The injector comprises a solenoid or a piezo element for electrically controlling a pilot valve. The pilot valve controls a flow of fuel to pressure-receiving surfaces of a valve piston, so that a tip of the valve piston is either pressed against ejection nozzles of the injector and blocks these or is withdrawn, allowing fuel to be ejected from the nozzles. Due to this principle of operation, only a fraction of the fuel that flows into the injector is actually injected into the cylinder. Fuel that has been used for driving the valve piston flows back to the tank, and so does fuel which escapes through internal leaks of the injector.
Fuel efficiency and pollutant emission rates depend critically on fuel injection timing. Not only must a predetermined quantity of fuel be injected into the cylinders at each engine stroke, but it must also happen at the right time interval (or intervals) during a stroke. Since the flow rate through the injector depends on the rail pressure (and other quantities), injecting the predetermined quantity of fuel may take longer than desired if the rail pressure is too low, or injection may stop earlier than desired if the rail pressure is too high. Further, atomization of the fuel depends on rail pressure. Non-optimal atomization may cause pollutant emission to increase and/or fuel efficiency to decrease. The fuel pressure that yields ideal atomization depends on the operating conditions of the engine, so that when these vary, the fuel pressure has to be adapted. For these reasons it is very important to control the fuel pressure. This must be done by controlling the operation of the pump so that at any time its delivery rate equals the rate at which fuel is drained from the rail by the injectors. The fuel drain rate is a rather complex function of operating conditions, since not only the engine speed, i.e., frequency of fuel injections may vary, but also the amount of fuel injected per engine stroke, and the leak rate of the injector depends on the duration of its excitation phases. Further, even if the fuel drain rate from the rail was exactly known, a pump can generally not be straightforwardly controlled to deliver this drain rate, since the pump also has internal leakage rates depending on input and output pressures and on fuel temperature, so that there is no one-to-one relationship between pump speed and delivery rate.
Conventionally, this problem is handled by experimentally analyzing the behaviour of the complete fuel supply system under a variety of operating conditions and tuning the control of the pump so that an appropriate fuel rail pressure is maintained in all operating conditions. This analysis and tuning has to be redone every time when the fuel supply system is modified, e.g., by replacing an injector or the fuel pump by one of a different type, requiring considerable amounts of labour.
At least one object of the present invention is to provide a control method and devices for carrying out the method which facilitate the integration of components having different characteristics into the fuel supply system. A further object of the invention is a controller for carrying out the control method and another object of the invention is a data processor program product. Furthermore, other objects, desirable features, and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.